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Atoms, Elements, and
Molecules
Image from: ase.tufts.edu
Matter
 Matter is anything that has mass and takes up
space
 Most of what we see is matter
 Matter is made of atoms
 What are atoms?
Atoms
 Atoms are the smallest building blocks
of matter that can chemically change
 This means that they are the smallest
piece of matter that has chemical
properties
 Since atoms make up matter, and matter
makes up almost everything we know, it
means almost everything is made of
atoms
 Atoms are made of different parts
Parts of the Atom
 The atom is made of basic 3 parts:

Protons
Both found in the nucleus

Neutrons

Electrons
‘Orbits’ outside the nucleus
Parts of the Atom - Nucleus
 The center of the atom is called the nucleus
 It holds all of the mass of the atom
 There are 2 parts of the nucleus:

Protons – positively charged

Neutrons – not charged
5
Parts of the Atom - Electrons
 Electrons ‘orbit’ outside of the
nucleus
 Electrons are negatively
charged
 Electrons weigh about 2000
times less than protons or
neutrons, so we assume the
nucleus has all of the mass
 Electrons orbit REALLY far
away from the nucleus
6
Electrons
 Electrons are really far away from the nucleus
 If the nucleus were the size of a marble and
that marble was placed on the middle of a
soccer field, the electrons would far outside
the outside of the stadium.
 This means that atoms are almost entirely
empty space
7
Atoms and Elements
 There are different types of atoms
 Each type of atom is called an element
 There are 92 naturally occurring elements
and 26 man-made elements
 Each element has it’s own unique physical
and chemical properties
8
Elements
 Elements are listed on the Periodic Table of
Elements
 Each elements has its own square on the
Periodic Table
 Each element has a 1 or 2 letter symbol
called a chemical symbol


The first letter is ALWAYS a capital letter
The second letter (if present) is ALWAYS
lower case.
9
Chemical Symbol Examples
 What are the
symbols for the
following elements?
1.
2.
3.
4.
5.
Hydrogen
Boron
Oxygen
Magnesium
Einsteinium
 What elements have
the following
symbols?
1.
2.
3.
4.
5.
6.
C
Ne
Kr
Mn
Au
U
10
Elements and Protons
 The number of
protons tells us the
type of element the
atom is


The number of
protons gives an
atom its identity
Protons are
abbreviated p+
 The number of
protons in the nucleus
of atom is the Atomic
Number
8
O
Oxygen
16.00
Atomic Number = Number of Protons
 The atomic number
MUST be a positive
integer
11
Element Examples
 How many protons do
the following elements
have?
1.
2.
3.
4.
5.
Oxygen
Fluorine
Titanium
Sodium
Silver
 Which elements have
the following atomic
numbers?
1.
2.
3.
4.
5.
24
58
11
100
3
12
Elements and Neutrons
 Neutrons are uncharged particles in the
nucleus

Neutrons are abbreviated n0
 When you add the number of protons with
the number of neutrons, you get the Atomic
Mass
8
O
Oxygen
16
Atomic Mass
13
Atomic Mass
8
Atomic Number = Number of Protons
O
Oxygen
16
Atomic Mass
 (# of p+) + (# of n0) = Atomic Mass
 Eg. Oxygen
 (# of p+) + (# of n0) = Atomic Mass
 (8) + (# of n0) = 16
 (# of n0) = 8
 Oxygen-16 has 8 neutrons in its nucleus
14
Atomic Mass Examples
 What is the atomic mass of the following
atoms?
1.
Nitrogen with 8 n0
2.
Calcium with 20 n0
15
Neutrons
 Elements always have the same number of
protons but can have different numbers of
neutrons in their nucleus
 The same element, with different numbers of
neutrons are called Isotopes
 Eg. All carbon atoms have 6 protons, but they
can have 6, 7, or 8 neutrons. Carbon-12,
Carbon-13, and Carbon-14 are all isotopes of
carbon
16
Atomic Mass Example
 Eg. How many neutrons are in the following
isotopes of Calcium?
 Calcium-40
 Calcium-42
 Calcium-48
17
Atomic Mass as an Integer
 Since the atomic mass is the
sum of 2 integers (number of
protons and number of
neutrons), the atomic mass is
ALWAYS an integer
 It is an irrational number on
your periodic table it is
because that is an average of
the masses of isotopes
18
Electrons
 Electrons determine the behaviour of an
element

They give an element its physical and
chemical properties
 The number of electrons is usually the
same as the number of protons
19
Electron Examples
 How many electrons
would the following
atoms have?
1.
2.
3.
4.
5.
Nitrogen
Helium
Potassium
Molybdenum
Bohrium
 What elements have
the number of
electrons?
1.
2.
3.
4.
5.
6
11
42
56
96
20
Electrons
 Remember when I said that atoms have the
same number of electrons and protons…
 That’s not always the case
Electrons
 Atoms can change their number of
electrons frequently
 This is because electrons are held loosely
by the nucleus
 This is also really important because if they
couldn’t, we wouldn’t be alive!
Electrons
 Atoms are called neutral if they have the
same number of protons and electrons
 This is because if an atom have the same
number of protons and electrons, the atom
has no charge

Eg. – Hydrogen
Has 1 proton and 1 electron
(+1) + (-1) = 0
No charge is neutral

Ions
 Atoms that lose or gain electrons are called
ions
 Ions have a charge
 When writing the charge, it always goes in the
top right-hand corner.

Eg. Fluorine with a -1 charge gets is shown as:
F
Eg. Selenium with a charge of -2 is shown as:
Se2-
Cations
 If an atom loses electrons, it gets a positive
charge
 Atoms with a positive charge are called
cations
Cation Examples
1) How many electrons would each of the
following have?


Beryllium loses 2 electrons
Sodium loses 1 electron
2) What is the charge on each of the following
atoms?


Aluminum loses 3 electrons
Silicon loses 4 electrons
Anions
 If an atoms gains electrons, it gets a
negative charge
 Atoms with a negative charge are called
anions

Think of it like this, A-Negative-ion, A-N-ion
Anion Examples
1) How many electrons would each of the
following have?
– Fluorine gains 1 electron
– Phosphorus gains 3 electrons
2) What is the charge on each of the
following atoms?
– Sulphur gains 2 electrons
– Chlorine gains 2 electrons
Can we go smaller?
 If matter is made of atoms; and atoms are
made of protons, neutrons, and electrons;
what are protons, neutrons, and electrons
made of?
 How small can we go?
Compounds
 So far we learned about elements, 1 type of pure
substance
 The other type of pure substance is a compound
 Compounds are 2 or more elements hooked
(sometimes called bonded) together
30
Compounds
 Compounds are made of 2 or more
combined elements
 However, they have completely
different chemical and physical
properties than the elements they are
made of
 Example – Sodium is a silver metal
that explodes when it touches water.
Chlorine is a poisonous gas that
destroys lung tissue. Sodium Chloride
is salt and is necessary for life
31
Chemical Formulas
 Molecules are another name for compounds
 All compounds are represented with a special
notation



Write the chemical symbol of each element in
the compound
If there is only 1 atom of that element in the
compound, leave it alone
If there are 2 or more atoms of an element,
write a small number in the bottom right hand
of the chemical symbol
32
Writing Chemical Formulas
 Example – Write the chemical formula for Calcium
Carbonate. It is 1 calcium, 1 carbon, and 3 oxygens.

Write the chemical symbol of each element


Ca C O
Write the number of the atoms in the bottom right
corner of the chemical symbol

CaCO3
33
Chemical Formula Examples
 Write the chemical
formula for each
compound
1.
2.
3.
4.
Hydroiodic acid – 1
hydrogen, 1 iodine
Hydrogen Peroxide
– 2 hydrogen, 2
oxygens
Glucose – 6 carbon,
12 hydrogen, 6
oxygen
Sulphuric Acid – 2
hydrogen, 1 sulphur,
4 oxygen
 Determine which
elements, and how
many of each, are in
the following
compounds
1.
2.
3.
4.
5.
BaCl2
N2
Fe2O3
KCo2F5
U3O8
34
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